Courtesy light fuse keeps failing

[70_F100_Custom]

Courtesy lamp fuse keeps blowing. I studied the wiring diagram and can't figure out what may be causing the fuse to fail. Has anyone had this problem before? Thought that I would check in here first before I go tearing the whole circuit apart.

[bluef250]

Start with the ground and work backward. Might be a blown bulb, or bad insulation on wire, or even the light switch. Do you courtesy switches on door frame?

[70_F100_Custom]

Yes I have the door frame switch. I have disconnected them and still the same thing. There is a large draw coming from something, and its not the cig lighter.

[68RGR]

You beat me to the cig lighter notion.

Mine was blowing that silly, little (2A?) dash light fuse.

Turned out the PO had installed a replacement cig lighter and connected the lighter LIGHT WIRE to the lighter GROUND terminal. You would've thought he might have had sense enough to relate the two events. But, he didn't!

Did you acquire the truck with this problem or is it something that happened after you owned it for a while?

If it is the latter, have you made ANY changes to the electrical system recently?

Check the dome light for a short. Seems to me that the dome light assembly and wiring is not of the best design.

In order to find my problem, I soldered a wire to each end of one of those little 2A (blown) fuses and connected a 12v bulb across it. That way, when the bulb went out, I knew I was on the right track. It was a whole lot cheaper than blowing fuse after fuse. NAPA wants about 80 cents a pop for those things these days.

If yours is one of the larger fuses, you might be able to use a couple of clip leads and a bulb.

Good luck.

[fordman]

the dome light wire runs from behind the instrument cluster up thedoor pillar and back over the door around behind the roof to thedome light. itmay have rubed ahole in the wire in that area. check the wire for rub spots. its grounding out someplace. it could be the bulb too. who knows. i guess it could also be the reostat on theheadlight switch. it could be grounding outto the base of the switch. remove either the instrument cluster or best yet the headlight switch and check the tang and reostat wire to see if it is ground to the metal base of the switch.

[bluef250]

The rheostat would cause the instrument lights to go out also. I agree that the way Ford ran the wire to cab light was poor and might be best location to look. Just find the 2 ends tie something on one end and gently pull the wire out. Check the wire for rubs, fix any, gently return.

[colnago]

Is there anything that you can do that will cause it, or prevent it? Does it always blow whenever you turn on the courtesy light? It's sounding like the wire has worn through and is grounding somewhere. But if you disconnect th cigarette lighter, does this keep it from popping? It's easy enough to check the switch with an ohmeter, or even a cheapie continuity bulb (but you should own an ohmeter or multimeter anyway).

Joseph